1. Field of the Invention
The present invention concerns a multi-beam x-ray device of the type having multi-beam x-ray tube and a diaphragm arrangement for fast acquisition of a plurality of x-ray images.
2. Description of the Prior Art
Conventional x-ray tubes are essentially composed of a vacuum chamber with housing in which a cathode and an anode are enclosed. The cathode acts as a negative electrode that emits the electrons toward the positive anode. The electrons are attracted from the anode and strongly accelerated by an electrical field between anode and cathode. The anode typically is formed of a metal, for example tungsten, molybdenum or palladium. When the electrons bombard the anode, their energy is for the most part converted into heat. Only a fraction of the kinetic energy can be converted into x-ray photons that are emitted by the anode in the form of an x-ray beam. The x-ray beam that is generated in such a manner exits the vacuum chamber through a radiation-permeable window made of a material with low atomic number.
Applications in industrial and medical imaging and for therapeutic treatments are unimaginable without x-ray tubes. All imaging methods with x-rays utilize the fact that different materials absorb x-rays differently. Conventional x-ray imaging methods generate a two-dimensional projection of a three-dimensional projection of a three-dimensional subject. The spatial resolution along the propagation direction of the x-ray beam is thereby lost.
Although it is also based on the different x-ray absorption properties of different materials, computed tomography offers a different form of imaging known as a slice image method. In computed tomography multiple x-ray images of a subject are generated from different directions and the lost volume information is subsequently reconstructed from these multiple images using a technique known as a back-projection method. Normally these 3D reconstructions are assembled from individual slices that proceed transverse to the subject. In this way a density can be determined for every volume element of the subject (known as a voxel, which corresponds to a three-dimensional pixel). A 3D image inside the subject can therefore be generated from all voxels.
In order to generate the multiple different slice images in computed tomography, an x-ray tube emitting the x-rays and an x-ray detector receiving the x-rays after exposure of the subject are moved around the subject. The mechanical movement is complicated and also occupies valuable examination time in medical technology. Various approaches have therefore been developed in order to be able to emit multiple different radiation beams from an x-ray tube. It is the goal to generate many slice images with different observation angles without mechanically moving the x-ray tube and the x-ray detector.
The PCT Application WO 25 2004/110111 A2 specifies a promising solution. A multi-beam x-ray tube with a stationary field emission cathode and an opposite anode are disclosed by this. The cathode comprises a plurality of stationary, individually controllable electron-emitting pixels that are distributed in a predetermined pattern on the cathode. The anode has a number of focal spots that are arranged in a predetermined pattern that is executed corresponding to the pattern of the pixels. A vacuum chamber encloses the anode and cathode. In one development, the cathode comprises carbon nanotubes.
The solution disclosed in WO 2004/110111 A2 offers many advantages relative to conventional thermionic x-ray radiation sources. It eliminates the heating element of the anode, operates at room temperature, generates pulsed x-ray radiation with a high repetition rate and generates plurality of beams with different focal spots.
In order to be able to use multi-beam x-ray tubes in medical technology, for example for a tomosynthesis in mammography, numerous adaptations are required. Among other things, it must be ensured that the radiation exposure of patients is minimized, the scatter radiation is reduced and the image series frequency is increased.